INVESTMENTS - Available-For-Sale Investments in Debt Securities, Perpetual Securities and Equity Securities (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 73,076	$ 69,072
Gross Unrealized Gains	8,504	8,722
Gross Unrealized Losses	1,384	1,092
Fair Value	80,196	76,702
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	70,261	66,363
Gross Unrealized Gains	8,129	8,432
Gross Unrealized Losses	1,313	1,035
Fair Value	77,077	73,760
Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,563	1,506
Gross Unrealized Gains	257	176
Gross Unrealized Losses	50	49
Fair Value	1,770	1,633
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,252	1,203
Gross Unrealized Gains	118	114
Gross Unrealized Losses	21	8
Fair Value	1,349	1,309
Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	35,815	32,459
Gross Unrealized Gains	4,728	4,951
Gross Unrealized Losses	489	261
Fair Value	40,054	37,149
Yen-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	668	624
Gross Unrealized Gains	63	83
Gross Unrealized Losses	10	2
Fair Value	721	705
Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	34,446	33,904
Gross Unrealized Gains	3,401	3,481
Gross Unrealized Losses	824	774
Fair Value	37,023	36,611
Dollar-denominated | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	584	579
Gross Unrealized Gains	55	31
Gross Unrealized Losses	11	6
Fair Value	628	604
Japan government and agencies | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	26,311	22,857
Gross Unrealized Gains	3,203	3,359
Gross Unrealized Losses	366	160
Fair Value	29,148	26,056
Municipalities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,322	1,295
Municipalities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	281	246
Gross Unrealized Gains	26	29
Gross Unrealized Losses	12	8
Fair Value	295	267
Municipalities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	901	894
Gross Unrealized Gains	133	142
Gross Unrealized Losses	7	8
Fair Value	1,027	1,028
Mortgage- and asset-backed securities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	504	1,337
Mortgage- and asset-backed securities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	272	1,096
Gross Unrealized Gains	32	33
Gross Unrealized Losses	0	8
Fair Value	304	1,121
Mortgage- and asset-backed securities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	184	196
Gross Unrealized Gains	16	20
Gross Unrealized Losses	0	0
Fair Value	200	216
Public utilities | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	7,843	7,683
Public utilities | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,637	1,533
Gross Unrealized Gains	324	318
Gross Unrealized Losses	6	3
Fair Value	1,955	1,848
Public utilities | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	5,296	5,205
Gross Unrealized Gains	669	690
Gross Unrealized Losses	77	60
Fair Value	5,888	5,835
Sovereign and supranational | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,386	1,469
Sovereign and supranational | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	846	862
Gross Unrealized Gains	133	186
Gross Unrealized Losses	6	5
Fair Value	973	1,043
Sovereign and supranational | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	326	335
Gross Unrealized Gains	87	91
Gross Unrealized Losses	0	0
Fair Value	413	426
Banks/financial institutions | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,545	6,063
Banks/financial institutions | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,551	1,420
Banks/financial institutions | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,039	2,673
Gross Unrealized Gains	414	403
Gross Unrealized Losses	83	74
Fair Value	3,370	3,002
Banks/financial institutions | Yen-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,315	1,266
Gross Unrealized Gains	208	128
Gross Unrealized Losses	50	49
Fair Value	1,473	1,345
Banks/financial institutions | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,680	2,570
Gross Unrealized Gains	513	507
Gross Unrealized Losses	18	16
Fair Value	3,175	3,061
Banks/financial institutions | Dollar-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	52	51
Gross Unrealized Gains	26	24
Gross Unrealized Losses	0	0
Fair Value	78	75
Other corporate | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	30,157	29,699
Other corporate | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	219	213
Other corporate | Yen-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,429	3,192
Gross Unrealized Gains	596	623
Gross Unrealized Losses	16	3
Fair Value	4,009	3,812
Other corporate | Yen-denominated | Perpetual securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	196	189
Gross Unrealized Gains	23	24
Gross Unrealized Losses	0	0
Fair Value	219	213
Other corporate | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	24,898	24,556
Gross Unrealized Gains	1,972	2,021
Gross Unrealized Losses	722	690
Fair Value	26,148	25,887
U.S. government and agencies | Dollar-denominated | Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	161	148
Gross Unrealized Gains	11	10
Gross Unrealized Losses	0	0
Fair Value	$ 172	$ 158